Ultrasound diagnostic equipment scans the inside of the subject with ultrasound waves and images the internal state of the subject based on received signals generated from reflected waves inside the subject.
Ultrasound diagnostic equipment such as this transmits ultrasound waves from an ultrasound probe to inside the subject, receives reflected waves generated from acoustic impedance mismatching inside the subject, and generates received signals. The ultrasound probe generates ultrasound waves by oscillating based on the transmitted signal and arranges in a scanning direction a plurality of ultrasound transducers that generate receiving signals by receiving reflected waves in an array configuration (for example, Patent literature 1).
The main configuration of conventional ultrasound probes is explained with reference to FIG. 11. Included is an ultrasound transducer 10 generating ultrasound waves, an acoustic matching layer (ML: Matching Layer) 20 reducing the acoustic impedance (AI) mismatch between the ultrasound transducer 10 and a living body from the ultrasound transducer 10 to the biological contact surface side, and an acoustic lens 30 converting the ultrasound waves. Moreover, from the ultrasound transducer 10 to the cable side, there is a substrate for signal withdrawal (FPC: Flexible Print Circut) 40 and backing material 50.
The acoustic matching layer 20 is established in 2 to 3 layers while gradually lowering the acoustic impedance AI from the ultrasound transducer 10 to the living body. ¼ wavelength λ is widely used as the thickness of respective acoustic matching layers 20. Here, the wavelength λ is the wavelength of ultrasound waves that transmit respective acoustic matching layers 20. Generally, materials with high acoustic impedance AI are hard and have good cutting ability; therefore, in order to reduce acoustic coupling with the adjacent elements, the acoustic matching layer 20 is simultaneously divided when the ultrasound transducer 10 is divided; however, materials with low acoustic impedance AI have poor cutting ability and slow sound speed, so the shape ratio (w/t) cannot be sufficiently reduced. Here, w is the width and t is the thickness. When w/t is close to 1, longitudinal waves are converted to transversal vibrations in the acoustic matching layer 20 within a marginal zone and interference between the two becomes unwanted vibrations, negatively influencing the transmission and reception characteristics of the ultrasound waves.